The present disclosure relates to a display, and more particularly, to a display having a color filter formed through an inkjet process, and a method of manufacturing the same.
Generally, color filters are used in flat panel displays such as liquid crystal displays (LCDs). The color filters are typically formed on an upper substrate of a multi-substrate structure where the upper substrate faces a spaced apart lower substrate and thin film transistors (TFTs) are formed on the lower substrate. However, to increase transmittance and reduce cost, a Color-filter On Array (COA) technique has been developed, where the color filters are instead formed on the lower substrate. Color filters are typically formed using a photolithography process, but studies are currently being conducted on methods of using inkjet processes to form COA structures so as to reduce cost.
When the inkjet process is used, ink containing a trichromatic pigment (e.g., one of R, G and B) suspended in a solvent is sprayed on a substrate in a corresponding image area so as to cause the area to be colored with the ink and so as to use the sprayed on ink layer after drying as a color filter. Through the inkjet process, it is possible to form superpixels each having pixel areas respectively colored for example with red, green and blue pigments where the different colorations are selectively deposited in corresponding pixel areas substantially at one time (one spraying operation). Therefore, a fabrication process can be significantly simplified, thus reducing fabrication cost.
In order to form the color filter using the inkjet process, viscosity or flowability or wettability of the utilized pigment fluid should be in a predefined range such as having a viscosity that is less than a predetermined first viscosity level so that the pigment fluid has good spreadability over an entire pixel region when spreading from sprayed-on points, and such that the viscosity is greater than a second viscosity level so that the sprayed on color filter solution does not spread too easily and overflow into an adjacent pixel region. To this end, a black matrix is often used to serve as a partition wall for the sprayed on color filter solution. In one class of embodiments, the pigment particles define part of a colloidal suspension and the particles are required to have good lyophobicity relative to each other (resistance to clumping or otherwise being re-dispersed due to proximity with each other) so as to prevent the color filter solution from clumping or agglomerating unevenly. Further to prevent the color filter solution from overflowing the partition walls, the partition walls themselves have a lyophobic characteristic relative to the pigment particles (being resistant to the suspension particles dispersing along the sidewall surfaces) so as to thereby function as a blockade that prevents the solution from whetting up and over the black matrix walls.
However, when a color filter is formed on a substrate in the above-described manner, a repulsive force occurs between the lyophobic black matrix material and the lyophobic color filter particles. As a result of this non-affinity between the black matrix sidewall surfaces and the colloidally suspended pigment particles, the color filter is not completely formed or filled in along edges of the pixel region, i.e., where the pixel area is closest to the black matrix sidewalls, so that a great difference in coloration thickness can develop between regions close to the black matrix and the other regions of the color filter that are further away. Such a variance in thickness of a color filter area is undesirable. Such a thickness difference of the color filter can cause light to be leaked due to undesired tilting of liquid crystals as shall be now explained in more detail.
More particularly, in one class of embodiments the color filter layer also defines a separation distance between a data line and a spaced above pixel-electrode of a pigmented pixel. The small thickness of the color filter at the edges of the pixel region gives rise to a change of capacitance problem especially in a COA structure where the color filters are formed on the lower substrate and define pixel-electrode to common electrode spacing. When the color filter with the small thickness is placed over a data line or in a region adjacent to the data line, coupling capacitance between a pixel electrode and the data line can also become non-uniform due to the lyophobicity induced change in color filter thickness, thus leading the structure to be vulnerable to a coupling-related hot spot problem.